Samsung SPH-A640 User Manual page 76

WARNING
911 Emergency Calling
Qwest recommends that TTY users make emergency calls by
other means, including Telecommunications Relay Services
(TRS), analog cellular, and landline communications. Wireless
TTY calls to 911 may be corrupted when received by public
safety answering points (PSAPs), rendering some
communications unintelligible. The problem encountered
appears related to TTY equipment or software used by PSAPs.
This matter has been brought to the attention of the FCC, and
the wireless industry and PSAP community are currently
working to resolve this.
58 Section 2B: Controlling Your Phone's Settings